Stupid question? Can I replace my torsionbars and leafsprings for coilovers?

Hemi Denny has a kit to replace the torsion bars...I have one installed on our 71 Dart. And GT Suspension aka Gerst has one also, and I am using that kit on the 71 Duster..

Those kit tend to use specific coil of shocks...due to the limited space on the front end.